It is Oct. 7 and the temperature has still not reached 32 degrees in Fargo-Moorhead. The first freezing temperature of the fall has happened in October for 13 of the past 16 years. The average first frost since 2000 is Oct. 3.
The average over the years 1900-1999 was Sept. 26. The average over the short period of record from the 1800s (1881-1899) was Sept. 16.
Of course, in any given year, the first frost might come early or late, depending on a variety of conditions including the jet stream pattern, soil moisture and the timing of clear and calm weather at night.
But the first frost of fall is obviously trending later. Some of this is due to the heat island effect of a growing metropolitan area. But because a similar, somewhat less extreme trend is evident at rural weather sites, our warming climate must be a portion of the cause.